1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor circuit or device having thin-film transistors (generally called TFTs) which circuit or device is used in an active matrix liquid crystal display and an image sensor.
2. Description of the Prior Art
In recent years, the technology of forming TFTs on an insulating substrate has been developed and is applied to manufacture of liquid crystal displays, image sensors, etc. Interlayer short-circuiting was a problem to be solved in developing such a technology. The technology of forming TFTs on an insulating substrate is similar to that of forming a semiconductor integrated circuit. However, these two technologies are different from each other in the following points, which are presumed to be causes of the interlayer short-circuiting problem.
First, because of the use of an insulating substrate, it is difficult to remove static electricity and, therefore, dust such as film forming dust likely attaches to a substrate. If an interlayer insulating film is formed without removing a dust piece attached to a substrate, the dust piece causes a pinhole when later peel off, reducing the interlayer insulation.
Second, because of the heat resistance of a substrate, the reflow technique for a phospho-silicate glass (PSG) cannot be used, which is commonly used in manufacture of semiconductor integrated circuits. Further, the methods of forming an interlayer insulating film are limited to plasma CVD and the like. Therefore, the step-coating performance is insufficient, and dust etc. likely occur during film formation. Insufficient step-coating performance likely causes cracks etc. in an interlayer insulating film, possibly resulting in interlayer short-circuiting.